The present invention relates to the general field of controlling the pitch of fan blades of a turboprop.
A preferred field of application of the invention is that of airplane turboprops having two propellers.
An airplane turboprop having two propellers comprises a turbine with two contrarotating rotors, each driving a set of unducted fan blades. In this type of airplane engine, the pitch of the fan blades constitutes one of the parameters used for controlling the thrust from the engine.
French patent application No. 10/51458 filed on Mar. 1, 2010 by the Applicant describes a system for controlling the pitch of fan blades of such a turboprop. In that document, each blade is coupled, for adjusting its pitch, to a blade root support that is pivotally mounted on a rotary ring via bevel gearing, one of the gearwheels of the gearing being supported by the blade root support and the other gearwheel carrying a counterweight. An actuator centered on the axis of rotation of the rotary ring and constrained to rotate with the turbine rotor is connected to each counterweight via a radial connecting rod. By actuating the actuator, the connecting rods act on the counterweights on the principle of a crank shaft and a connecting rod so as to cause the blade root supports to pivot in synchronized manner.
Such a control system presents numerous advantages. In particular, it is reliable and light in weight since it possesses relatively few parts compared with prior art control systems.
The connecting rods of the system extend radially from the actuator to the blade root supports. As a result, some of those connecting rods need in particular to pass through an oil enclosure in which various rolling bearings of the turboprop are housed. This applies in particular for the connecting rods of the system for controlling the upstream set of blades.
Unfortunately, such oil enclosures rotate in operation, and as a result the oil that is present therein is subjected to centrifugal force. Consequently, in order to prevent any outward leakage of oil from the oil enclosure, it is necessary to seal the packages where the connecting rods of the control system pass through the partitions of the oil enclosure.